Electric hygrometer



Oct. 31, 1939. w. F. ALDER ELECTRIC HYGROMETER Filed Nov. 10, 1936- 4 Sheets-Sheet 1 WNW m EM In V611 tor.

24 H i iorneys.

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Oct. 31, 1939. w. F. ALDER 2.177.630,

ELECTRIC HYGROMETER Filed Nov. 10, 1936 4 Sheets-Sheet 2 H iiomeys.

Filed Nov. 10, 1936 4 Sheets-Sheet 3 www MVN

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Oct. 31, 1939. w E ALDER 2,177,630

ELECTRIC HYGROMETER Filed Nov. 10, 1936 4 Sheets-Sheet 4 Fzq. 9.

Attorneys.

Patented Oct. 31, 1939 UNITED STATES PATENT OFFICE ELECTRIC HYGROMETER.

Application November 10, 1936, Serial No. 110,;31

12 Claims.

I designate my invention as an electric hygrometer as I make use of certain electrical phenomena in obtaining hygrometric measurements. The instrument therefore which I have discovered and invented makes use of the electrical phenomena of an electric thermo-couple which records or indicates differential temperatures and coupled with this I employ an integrating device having hygrometric tables so that the relative humidity may be obtained for any temperatures between predetermined range limits. The relative humidity may be indicated or a record may be made thereof or a signal device operated to give a warning or to operate by relays a suitable control for mechanism to be operated when the relative humidity deviates from a predetermined value at the range of temperatures desired.

An object and'features of my invention is the construction and development of a compact and unitary instrument which determines the relative humidity of the air or if desired other gases and may be used in conjunction with so-called air conditioning, this feature of air conditioning including providing the proper amount of moisture in the air between specific temperature ranges. As above mentioned the instrument may be used either to indicate or record the changes of humidity values or by suitable relays to control the operation of auxiliary machinery to provide moisure for an air circulating plant.

In view of variable factors entering into a relative humidity, such as the relative humidity being different at low and high temperatures for the same actual amount of moisture in the air, it is necessary to compensate or have the machine integrate for this purpose in accordance with changing temperatures. In my invention I make use of the different temperatures developed by the use of so-called dry and wet bulb thermom eters, but as the ordinary thermometers are not sufficiently delicate or accurate, I use a thermoelectric pile for this purpose. Therefore one of the objects and features of my invention is developing a thermo-electric pile to generate thermo-electric current by the medium of two elements subjected to a difference of temperature, one of which is exposed to preferably circulating air and the other exposed to the same air but cooled by the evaporation of water therefrom, such water being preferably drawn from a reservoir by a suitable wick. A'n indicating instrument is operated by the thermo-electric current and will indicate a potential difference between the two sides of the thermo-pilc. A further detailed feature of my invention is forming the thermo-pile in conjunction with two silver tubes which are similar in structure and mounting except that one tube is encased or connected to a wick, this being continually moistened by water from a reservoir. These silver tubes each have a thermo-series adjacent thereto but preferably electrically insulated from the tubes so that a change of temperature of each couple develops its own electric current. These couples are connected together to develop a differential potential between the two sets of junctions or what might be termed between the two sides of the thermopile assembly.

A further object and feature of my invention includes an indicating instrument preferably having a pointer actuated by the thermo-electric current, this being in the form of a micro-ammeter which indicates slight changes of the temperature between the two silver tubes or similar devices.

Another object and feature of my invention involves developing a movement in a hygrometric chart or tables of humidity so that as the temperature changes the table will be moved to position the correct set of humidity numbers to register with the pointer actuated by the thermoelectric pile. A further detail feature of my invention relates to the specific construction of the chart or table involving the humidity numbers being arranged in a series of arcs or curves to form a proper registry with the end of a pointer oscillating on a pivot as regards temperature dilference between the air temperature and wet series values.

Another detail feature of my invention thus includes a temperature responslve device in which a partial drum or partial cylinder including a chart is moved in an arc by changes of temperature of the same air to which the wet and dry tubes are subjected. A relatively simple way toaccomplish this is to employ thermostatic elements which by their expansion and contraction due to temperature changes, cause a rotation of the cylindrically arranged chart. This may be accomplished by having a series of temperature responsive coils acting on a single instrument for rotating the chart. Thus by having a series of such temperature responsive devices, a compensation is made for inaccuracy in any one of the devices. It is within the scope and spirit of this invention to use a plane chart moved vertically by a suitable series of levers which are actuated by a simple iii-metallic element in lieu of the spiral elements shown.

the accompanying drawings, in which:

Fig. 1 is a front elevation taken in the direction of the arrow l of Fig. 2 with the cover casing broken away.

Fig. 2 is a side elevation with the casing in section taken in the direction of the arrow 2 of Fig. 1.

Fig. 3 is a rear elevation taken in the direction of the arrow 3 of Fig. 2.

Fig. 4 is a vertical section from front torear taken substantially on the sectibn line 4-4 of Fig. 1 or 3 in'the direction of the arrows.

Fig. 5 is a partial elevation taken in the direction of the arrow 5 of Fig. 2 of the thermometric operating mechanism for the chart.

Fig. 6 is a detail vertical transverse section on the line 8--6 of Fig. 5 in the direction of the arrows showing one of the thermo-metric coils.

Fig. 7 is a detail horizontal section taken substantially on the line 1-7 of Fig. 3 or 4 of the thermo-electric assembly having the wet and dry tubes with parts omitted to show the connection of the thermocouples.

Fig. 8 is a perspective view taken substantially in the direction of the arrow 8 of Fig. 5 showing a portion of one of the quadrants for mounting the chart.

Fig. 9 is a developed view of the chart.

Fig. 10 is an electrical diagram showing the thermo-electric series with the wet and dry tubes, the pointer actuated by the current developed thereby and the electric relay control by the pointer.

Fig. 11 is a plan of the top of a cover case taken in the direction of the arrow ll of Fig. 1 or 2.

Fig. 12 is a horizontal section on the line I 2-l2 of Fig. 1 or 2 taken in the directioh of the arrows.

Fig. 13 is an elevation similar to a portion of Fig. 1 showing a capacity or condenser type of circuit between the pointer and condenser strips on the chart, this figure being more or less diagrammatic.

Fig. 14 is an end elevation of Fig. 13 taken in the direction of the arrow, also shown in a diagrammatic manner.

Fig. 15 is a diagram of a thermocouple between the wet and the dry tubes instead of the thermopile as illustrated in the diagram of Fig. 10.

In my instrument I employ a frame structure I! (note particularly Figs. 1 to 4) which has a central upright casting [2, this being in the form of a wide vertical partition plate [3, having two marginal webs l4 projecting forwardly, there being also a plurality of journal ears [5 extending forwardly from the outer side edges of the plate and forming a reinforcement of the webs II. The plate has two central openings IS with a curved cover panel I! attached adjacent the margins thereof to prevent. a draft of air effecting the electrical parts of the apparatus. This panel I! is on the rear side of the plate. On the forward side of the plate there are two vertical plates ill with arcuate slots l8 to which the thermo-metric coils are attached as hereinunder detailed and over this is a cover cap 19 attached to the front of the plate 13 to protect the thermometric coils from the air draft.

A fiat base 20 forms the support for the frame II, being preferably formed integral with the central upright casting l2. A water reservoir 2i connects the base and the frame [2. This is defined as having a top 22 and sides 23 with an opening 24 in the bottom closed by a removable 'means 36 for an electric motor housing 31.

My invention is illustrated in connection with clean-out plate 25, this having a water tight joint. At one side of the reservoir there is a filling cup 26 open at the top for supplying water to the reservoir. The reservoir is also provided with a lateral extension 21 having an opening II for a wick as hereinunder described, this extension being on the rear side of the partition plate ll.

Extending outwardly from this partition plate It on the rear side thereof there is a wide fln 29. I

This connects with the top of the reservoir and has horizontal flanges ill for reinforcement.

An electric motor support 3| has a sloping plate structure 32 extending laterally from the upper part of the casting l 2, preferably formed integral therewith, this extending the full width of the casting I2 forming a relatively large recess 31 on the front side of the partition II at the top of the instrument frame. A secondary frame structure ll includes a bracket 35 with an attaching This housing contains an electric motor with a fan shaft 38 and a fan 39 of the propeller blade type positioned to direct a draft of air downwardly, the sloping plate structure 32 causing the draft of air to be directed downwardly on the rear side of the vertical partition plate i3 for purpose hereinunder detailed.

The thermo-metric operating mechanism designated by the assembly numeral is shown particularly in Figs. 4, 5, and 6. This includes the oscillating shaft 5| which is journalled preferably in bushings such as 52 in the marginal webs H and the ioumal ears 15 or if desired, only in the Journal ears. At the center portion of the shaft there is a hub 53 having a series of bi-metallic thermo-metric coils 54 connected thereto. Each coil as indicated at Fig. 6 has its inner end Bl secured to the hub and coiled thereabout in a spiral type coil. The fixed end 56 is attached to a shiftable rod 51 extending through the arcuate slots iii of the plates II; and when aligned with graduations 58 is secured with nuts 59, providing a setting for coils 5|. A number of these coils are used for the purpose of averaging any'air which a single thermo-metric element might interpose. These coils are covered by the cover cap I! but are subject to the atmospheric temperature of the place in which the instrument is used. Secured to the shaft Si is a quadrant assembly 6!. Each quadrant has a hub 81 clamped to the shaft by set screw G2 or the like and has radially diverging arms 63 connected by a segmental curved quadrant 64. The inner edge of each quadrant has a groove 65 concentric with the shaft (note Fig. 8). A static and dynamic balance is given to the quadrants by a balance arm and weight assembly 10, there being two of these assemblies, each having a hub ll (note Figs. 4 and 5) secured to the shaft 5| by a set screw 12 or the like and having a series of radial arms 13. which are screw threaded and on which are mounted adjustable weights 14 which weights, when properly adjusted, may be secured by set screws or any other suitable manner. The curved cover panels I! protect the weights from the down-draft of air caused by the fan. A chart 15 is formed of stiff paper or cardboard such as Bristol board and has its two marginal edges 18 fitted in the grooves 65 of the quadrants. The chart is thus curved and forms a section of a cylinder (note Figs. 1, 2 and 4). On account of the static and dynamic balance above described, the chart and the shaft on which it is mounted may readily turn in an up and down direction indicated by the reversed arrows ll of Fig. 4 in accordance with the changes of temperature of the air at the place in which the instrument is installed, the coils 54 expanding or contracting with the temperature as is well known in such thermo-metric temperature indicators. It is to be noted that the chart and all of this balanced mechanism of the thermo-metric indicating device is adequately screened from the down-draft of air from the fan and thus is responsive solely to temperature changes in the movement of the chart. The details of the chart are given hereinunder.

The thermo-electric series designated by the assembly numeral 85 includes two silver tubes 88, (note Fig. 7) these each having a longitudinal slot 81 with integral flanges 88 extending towards each other to receive the thermopile 89 (note Fig. 10). This thermopile is formed of alternate strips of iron and constantan wire converging to the opposite tubes and an iron and constantan strip or ribbon being connected together at their point of contact in any suitable manner. I find it satisfactory to have sixty couples with thirty junctions on each side. The junctions are held between the flanges 88 by celluloid 89', this being molded from liquid celluloid which hardens and forms an electrical insulation of the thermopile or couple from the silver tubes but has a good heat transference connection through the celluloid. One of these tubes indicated at 90 has a polished exterior surface without a cover whereas the opposite tube 9| similarly polished, is covered by a wick'82. The wick is formed of a strip of fabric 93 curved around and in close contact with the outside of the tube 9| and held in place by a spring clip 94 (note Figs. 3, 4 and '7). This clip has an eye 95 at the top and two prongs 98 clamping the longitudinal edges of the wick adjacent the flange 88. The wick has a downward extension 91 which passes through a ferrule 98 above the opening 28 of the extension 21 of the reservoir 2I and thus dips into the water in such reservoir. Both of the tubes, that is, the polished tube and the tube having the wick, are exposed to the downward draft of air from the fan. As the tube with the wick is cooled by evaporation of water from the wick, the two tubes function somewhat as a wet and a dry thermometer commonly used in hygrometric tests of air. the tubes and the wick are stationary with *the air circulating past these. The change in temperature of the tube 8| having the wick thereon cause the development of a thermo-electric current in the grid structure of the thermopile wires or strips.

The resultant current develops a circuit in the wires I05 (note the wiring diagram of Fig. 10), there being a lead I08 from the upper connection of the grid and a lead I01 to the lower connection. These leads connect to an instrument of a micro-am'meter type I08. This is illustrated in the diagram of Fig. 10 as having a field magnet I09 with a rotatable armature coil I I mounted on pivots III situated between the poles of the magnet. The lead I08 connects as indicated at II2 to one end of the coil IIO'and the lead I01 connects at II3 to the opposite end of this coil. These leads have a flexible section to permit free rotation of the armature coil. A pointer arm I I4 is connected to the armature to move therewith and. has an electric contact end II5 to close an electric relay circuit hereinunder described.

In the relay circuit designated by the assembly numeral I20 I use a contact wire I2I connected In this case however,

to the chart and extending thereacross in a diagonal manner from the upper to the lower edge, this wire however being spaced from the chart in order to be engaged by the contact end I I5 of the pointer. This pointer is electrically connected to a hair-spring conducting wire I22 from which extends an electric lead I23. One end, preferably the lower end of the chart wire I2I indicated at I24, is insulated but the opposite end, that is, the upper I25 is connected by an electric lead I28 to an electro-magnetic relay I30 (note Fig.

A current supply device designated I35 (note Fig. 10) is used to generate or supply current for the relay I30, This may be any suitable type device for supplying a low amperage current. In the construction shown I illustrate a grid I38 forming a thermo-electric pile. This may be constructed by using two tubes or U shaped metal plates I31 and I38 with the wires forming the thermopile formed of alternate strips of iron and constantan metal arranged somewhat as the thermopile 89, the wires being connected much as shown in Fig. 'I. In this case however, the tube or connecting strips I38 are positioned to be heated by the field winding I39 of the fan motor I40 mounted in the motor housing 31. The field is energized by a circuit I which may connect to an alternating current line. In the illustration shown the electric lead I23 connected to the pivoted end of the pointer II4 connects at I42 to the thermopile grid I38. The opposite end I43 of this grid has a lead I44 which connects at I45 to the armature winding I48 of the relay I30. lead I28 from the contact wire I 2| connects at I41 to the opposite end of this armature coil. The relay is indicated as having a field magnet I48.

The relay I30 may be bi-polar by having two fixed or adjustable contacts I80 and I8I to be engaged by a moving contact I82 on the movable pointer arm I83 secured to the pivoted coil I48, this coil being mounted in the usual manner on pivots. A spring I84 retains the pointer in its neutral position. In the illustration a lead I85 connects from one of the contacts I80 and a second lead I88 from the pivotal point of the pointer I83, These lead to an external circuit notv illustrated, for either giving a signal or operating a relay for controlling certain mechanism, which for instance may be connected to an air conditioning plant.

The operation of the device as so far described is substantially as follows: In accordance with temperature changes in a room or place in which the instrument is installed, due to the action of the thermo-metric coils 54, the.chart is moved up or down in the direction of the reversed arrow 11 of Fig. 4. This alters the point of contact of the diagonal wire I2I mounted on the chart with the contact point II5 of the pointer arm 4 of the micro-ammeter device I08. As above mentioned, this pointer is moved due to the electric current developed by the thermopile 89 which is influenced by the wet and dry silver tubes 90 and 9|. The power source I35 having in this instance thermo-electric couples, supplies the direct current passing between the contact point II5 of the pointer arm I I4 and the contact wire I2I mounted on the chart. On this contact being made the armature coil I48 of the relay I30 is energized and causes a movement of the pointer arm I83 of the relay thus bringing the contact I82 into engagement with one or other of the contacts I80 or I8I and hence establish- The' This causes the whole chart to have a cylindrical curve. Adjacent the left hand edge of the chart there is a'vertical temperature column I", this being indicated in from. 30 to 120 degrees E, that is, jumpsoi 10 degrees and the chart is constructed from United States Government bygrometric charts. However instead of the relative humidities for each temperature being arranged'in a horizontal row there are a series of curved or arched lines Ill. These are all on the same curvature, that is, have the same radius, such radius being defined as the length of the pointer III so that the contact end of this pointer for any particular temperature will follow one of, these arched lines. The relative humidity tables also have a series of vertical columns I12. The contact wire I2I is illustrated as being stretched across the chart in a line approximating a relative humidity of 60. It will be noted that it is necessary to interpolate between adjacent humidity figures of the various curved lines. meral is indicated by a dot III below each humidity numeral. Such wire is secured to the chart in any suitable manner, being spaced slightly above the chart and has a lower end support I 24 and the upper lead connection I25. this latter being shown as connected to the electric lead I26 (note Hg. Manifestly if it is desired to make the electric contact between the pointer end II! and the chart wire I2I at different humidities, the wire will be arranged in a different manner on the chart. It is therefore preferable in a laboratory to attach wires such as Hi to a series of different charts to have a position corresponding to difierent humidities.

The reference point of each nu- Itis also manifest that if the pointer end II! isto operate between minimum and maximum humidities, that it will be necessary to have two wires such as I2I, one of which would follow the low humidity figures and the other the high humidity figures. In this case the moving contact I62 of the relay Ill would make a contact with the adjustable contact Iii as well as the contact I" depending on whether the humidity were low or high and it would be necessary to run a lead wire corresponding to I85 from the contact IBI and making a connection in an external circuit corresponding to I85 and I".

In Figs. 13 and It I show a condenser or ca pacity assembly designated IIIII which is alternative to using a contact wire such as I2I. In this case I employ one or two condenser strips Ill and I82 which may be made of silver or aluminum foil about .001 inch in thickness. These are secured tothe underside of the chart I! with the average desired humidity curve midway between the two strips. The pointer Ill has a condenser plate I83 which may be of silver or aluminum foil and.is thus positioned above the paper or card board chart. Suitable electrical connections are made from the ends of the foil strips IOI and I82. A circuit suitable for connection through the pointer and to the ends of the strips is a standard grid glow tube circuit in which a grid glowtube acts as a relay and in which the capacity change disturbs the voltage and fires the tube. It will be obvious that by a suitable amplification the current through the on a wall or the like.

tube may be amplified in standard and known manners.

In Fig. 15 I show a thermocouple III instead of the thermopilej! of Fig. 10. In this I use the polished silver tube '0 and a similar tube with a wick 9|. The thermocouple may consist for instance of a constantan wire I" forming a thermal connection to the two tubes much asshowninFlg'landtheleads SI and lllmay be formed of iron wire to develop the two ends of the thermocouple.

As it is convenient to have a signal to show the water level in the reservoir II, I employ a water signal mechanism designated by the assembly numeral I" (note particularly the diagram of Fig. 10). This includes a fioat Ill attached to a pivoted arm "2 (note Figs. 3 and 4). Thisarmisindicatedaspivotedat llltoa'flxed structure preferably the top of the reservoir, there being an opening for the passage of the arm. The upper end of'the arm has a switch supporting portion I94 on which I mount preferably a mercury switch III. An electric lamp I 96 is connected in the .circuit of the switch. The signal circuit is indicated in Fig. 10 as having one lead I91 and a second lead I, these being hooked to the opposite sides of the supply current line I. The float and switch are arranged so that when the water level drops to a predetermined point due to the evaporation from the wick 92, the lamp signal is given, thus indicating that the reservoir should be replenished.

In the above description of my invention I have not designated in detail a construction for covering or protecting the operative parts of the instrument. -However, it is desirable to provide a cover or case designated by the assembly numeral 2". This may be considered as having a front wall 2 with a projecting portion 2I2 for the electro-magnetic relay Ill. A glass window 2 allows inspection of the position of the pointer I63 of this relay. A second and arch shaped window 2] is positioned in front of the chart so that the position of the pointer end of the pointer arm Ill in relation to the chart may readily be inspected. This also allows observation of a fixed temperature indicator III (note Fig. 1) and attached to a fixedpart of the instru;- ment and pointing to the temperature column I" of the chart I". A third or lower window 2I6 is located in frontof the signal lamp Ill. ThebackZII ofthecasecoverstherearportion of the instrument assembly forming a cover for the assembly 85 of the thermo-electric series. The side walls 2|! and 2|! form suitable covers for the side of the instrument, the filling cup 2| projecting through an opening in one side and having a cover lid 22!. The front and back portions of the cover are preferably made with a vertical joint 22I for removal from the frame of the instrument. The top 222 is provided with a series of screened openings 223 and is provided with a threaded knob 22 which may function to attach the front and rear portions of the frame together at the top joint 225. The base 226 of the cover is provided with a series of opening and the instrument may be suspended It will therefore be apparent that the electric fan II develops a downward flow of air which is confined to the rear portion of the instrument back of the casting I2. This subjects the, two silver tubes II and II to the downflow of an we thus the wick l2 has continuous air fiow th'ereover to facilitate the evaporation of. the water from the wick. The

quadrant assembly 60 having the chart and the thermo-metric coils 54 are maintained in still air. However, there is sufficient space forming a non-draft communication between the front portion on the instrument and the back portion so that the air surrounding the thermometric coils 54 is of the same temperature as the air flowing over the wick and the dry tube 90.

By the construction above described it will be noted that my invention comprises two main devices in which one may be considered as the humidity responsive assembly in which the thermo-electric current operates the electro-magnetic instrument having the pointer. The second includes the temperature responsive assembly having the chart moved by thermo-metric devices. It is believed obvious that the chart and pointer might be interchanged, that is, that the humidity responsive assembly developing the thermo-electric current could be used to move the chart and thermo-metric coils or the equivalent utilized to move the pointer, the chart and pointer being arranged contiguous for integrating the humidity values for different temperatures. It will also be apparent that the pointer and the chart operate as indicating instruments showing the relative humidities for different temperatures but it is also apparent that the chart could be omitted and a device prepared having either a conducting wire as shown in Fig. 4 or the combination of conducting and capacity elements as shown in Figs. 13 and 14, for when the instrument is used for giving a signal or operating a relay, the chart itself is not essential for direct application to the instrument.

It is believed that a simplification of my device is quite obvious in that the movable pointer H4 of the humidity responsive device may be considered by its movement of giving an indication of the temperature differentials of a wet and dry thermometer used for determining hygrometric values. This pointer may be moved over a chart having a temperature numerals thereon and numerals for the various humidities, then this chart may be manually shifted in accordance with the particular air temperature at the time in which the pointer is being influenced by the differential' temperatures of the dry tube 90 and the wet tube 9| having the wick 92 or the equivalent.

Various changes may be made in the details of the construction without departing from the spirit or scope of the invention as defined by the appended claims.

I claim:

1. In a device as deseribed, the combination of a first instrument assembly having a wet and a dry element with means forming a thermoelectric couple therebetween in accordance with the air humidity, an electro-mechanical device operated by the thermocouple current, a second instrument assembly including a movable chart having a table of humidities for difierent temperatures, a thermo-metric means to move said chart, the chart and an indicating portion of the electro-mechanical device being relatively positioned to designate the particular humidity for a predetermined series of temperatures, a signalling assembly having one part including the indicating portion of the thermo-electric device and another part operatively connected to the chart arrangedto give a signal at substantially the same degree of humidity for different temperatures.

2. In a device as described, the combination hygrometric table with of a humidity influenced assembly including similar structural elements, a wick forming a covering for one of the elements, means to maintain the wick moist with water, means to subject both elements with the wick to circulating air, means to produce a thermo-electric current due to the differential temperatures of the said elements, an electro-mechanical indicator operated by such thermo-electric current, a temperature responsive assembly including a movable chart having a hygrometric table thereon, such table having numerals for different temperatures and other numerals for humidities at each temperature, means to move the chart in accordance with changes of temperature of the air influencing the said elements of the humidity influenced assembly, the said chart and the electro-mechanical indicator being positioned whereby said indicator registers on the chart with the correct humidity numeral for the specific air temperature; one or more electric conductors arranged contiguous to the chart and conforming in position to substantially constant humidity values, a source of a secondary current, means to close the secondary circuit through part of the electro-mechanical indicator and one of the conductors to produce the secondary circuit at substantially constant humidity values but over different temperature ranges.

3. In a device as described, the combination of of a humidity influenced assembly including a pair of similar structural elements, a wick covering one of the said elements, means to maintain the wick moist with water, means to subject both elements to circulating air, thermopile wires thermally but not electrically connected to the said elements to be influenced by the difference of temperature between the element having the wick and the element without the wick to produce a thermo-electric current, an ,electromechanical indicator having a movable pointer operated by such thermo-electric current, a temperature responsive assembly including a chart having a hygrometric table, a supporting means for the chart curving the chart to form part of a cylinder, a thermo-metric device operatively connected to the chart supporting means to oscillate the chart in accordance with changes of air temperature, the said chart having a table with a column having temperature numerals and a series of arcuate lines having numerals of different humidities associated with the temperature numerals, the pointer having its free end positioned contiguous to the chart to conform in its movement to the curved lines of numerals of the humidities and thereby register with the particular humidity numeral for the particular air temperature.

4. In a device as described and claimed in claim 3, the chart having one or more electrical conductors positioned contiguous thereto, said conductor or conductors being positioned on the chart to conform to the same humidity value for different temperatures, a power source for a second electric circuit, the second circuit hav ing a connection through the pointer and through the conductor to establish the second current through the pointer and one of the conductors when the air has the same humidity value for different temperatures.

5. In a device as described, the combination of a humidity influenced assembly including a pair of similar structural elements with means for evaporating water from one element and maintaining the other element without evaporation to develop a diiference of temperature between said elements, means to produce a thermoelectric current due to the differential temperatures of the said elements, an electro-mechanical instrument having a movable element operated by the thermo-electric current, a movable supporting structure having one more electric conductors, a thermo-metric means to move the support and the conductors, the conductors and a pointer part of the movable element oi? the electro-mechanlcal device being positioned ,ior registry whereby the conductor or conductors conform to a path of contigui y with thesaid pointer part of the movable element to define substantially constant humidity values for changes or temperature, an electric power source with a connection through the movable element and the conductor or conductors to produce a cloud circuit when the pointer end of the movable element is closely contiguous to one of the conductors.

6. In a device as described and claimed in claim 5, the conductor or conductors being positioned and mounted to rotate in an are around a first axis, the pointer part of the electro-mechanical device being positioned to be rotatable about a second axis, the two axes being at right angles one to the other.

7. In a device as described, the combination of a supporting structure, a hygrometric chart mounted thereon, said chart having a table with a vertical column of numerals giving diirerent temperatures and a series of arched lines of humidity value numerals, there being an arched series of numerals for each temperature numeral and means to move the supporting structure with the chart whereby difierent humidity values may be interpreted for varying temperatures.

8. In a device as described and claimed in claim 7, the chart having one or more electrical conductors positioned contiguous thereto, the conductor or conductors being arranged approximate to the same humidity values for different temperatures and means operated by temperature changes to establish an electric circuit through one 01' the conductors.

9. In a device as described, the combination oi a supporting structurea hygrometric chart mounted thereon forming p rt of the periphery of a cylinder,- said chart having a table with at least one column of numerals arranged peripherally of the chart and giving difierenttemperatures and a second series or numerals arranged in arched lines considered somewhat longitudinally, of the chart and designating humidity.

numerals for each temperature, a pointer arm having a pivot at right angles to the axis of the supporting structure and thus of the cylinder of the chart and having a free end movable over the chart, means to rotate the chart in accordance with changes 0! air temperature and means' to move the pointer in accordance withchanges of air humidity whereby the free end oi the pointer may register with the arched lines o! humidity numerals and thus indicate the humidity at a specific temperature, the chart having an elongated electrical conductor forming a line relative to the cylindrical periphery of the chart and also conforming to the same relative humidity for different temperature values, the free end or the pointer having a contact to engage the said conductor and thus form a closed contact for an electric circuit through the conductor and the contact.

10. a device, as described, the combination of a ovable supporting structure having an elongated electrical conductor positioned thereon and having a shape to define substantially the same relative humidities for varying temperatures, means to move said structure and thus the conductor in accordance with changes 0! air temperature, an electrical contact, means to bodily move said contact in accordance with changes of air humidity whereby the contact and the conductor may engage and thus complete a connection for an electric circuit through the conductor and'the contact.

11. In a device as described the combination of a first circuit forming means to develop a first changing electric current in accordance with the humidity of the air, a first circuit closing means operated by the first electric current, a second and complementary circuit closing means with a control therefor operated in accordance with the changing temperature of the air, the first and second circuit closing means being positioned to close a circuit at predetermined relationships of temperature and humidity and means to develop *a second'electric current through the first and second circuit closing means whereby the second current is established at varying humidltles and at varying temperatures.

12. In a device as described the combination of an electro-mechanical device having a movable indicator, means to actuate said device by an electric current produced through diilerential temperatures resulting from evaporation of 1711- ter and non-evaporation of water from similar structural elements, a chart having a y metric table thereon, means to move said chart in accordance with the change of temperature of the air'to which said elements are subjected. a mounting means to support the said movable indicator elements and the chart to locate the indicator and chart to indicate diiierent air humidities on the chart for difierent air temm tures, means forming a second electric circuit having a source of power and a circuit closing means actuated by the relative position 01' the indicating means and the chart whereby a second electric current is developed at substantially the same degree 01' air humidity i'or a, series of different air temperatures.

7 WILLIAM F. ALDER. 

